Re: misunderstanding of spare and raid devices? - and one question more

[David Brown <david.brown@hesbynett.no>]

On 02/07/11 10:34, Karsten Römke wrote:
> Hi Phil,
> I have done some tests and appended the results, maybe they are of interest
> for somebody. As a conclusion I would say raid5 and raid6 make in my
> situation
> nearly no difference.
> Thanks to all for hints and explanation
> Karsten
>

If raid6 doesn't have any noticeable performance costs compared to raid5 
for your usage, then you should definitely use raid6 rather than raid5 + 
spare.  Think of it as raid5 + spare with the rebuild done in advance!

mvh.,

David



>
>
> --------------------------------------------------------------------------------------
>
> first - just copy a dir with a size of 2,9 GB, it was copied once before
> so I
> think there are still data buffered?
>
> OLDER war im Cache? hatte Dir vorher kopiert
> kspace9:~ # date ; cp -a /home/roemke/HHertzTex/OLDER/* /raid5/ ; date
> Fr 1. Jul 16:15:57 CEST 2011
> Fr 1. Jul 16:16:26 CEST 2011
>
> kspace9:~ # date ; cp -a /home/roemke/HHertzTex/OLDER/* /raid6/ ; date
> Fr 1. Jul 16:17:27 CEST 2011
> Fr 1. Jul 16:17:58 CEST 2011
>
> --------------------------------------------------------------------------------------
>
> now a test with bonnie, I found this example online and the parameters
> seems
> senseful to me (I've never done performance tests on hd's before, so I
> searched
> for an example)
> bonnie, found
> -n 0 : file creation 0
> -u 0 : root
> -r : memory in megabyte (calculated to 7999)
> -s : file size calculated to 15998
> -f : fast, skip per char IO-tests
> -b : no write buffering
> -d : set directory
>
> kspace9:~ # bonnie++ -n 0 -u 0 -r `free -m | grep 'Mem:' | awk '{print
> $2}'` -s $(echo "scale=0;`free -m | grep 'Mem:' | awk '{print $2}'`*2" |
> bc -l) -f -b -d /raid5
> Using uid:0, gid:0.
> Writing intelligently...done
> Rewriting...done
> Reading intelligently...done
> start 'em...done...done...done...
> Version 1.03d ------Sequential Output------ --Sequential Input- --Random-
> -Per Chr- --Block-- -Rewrite- -Per Chr- --Block-- --Seeks--
> Machine Size K/sec %CP K/sec %CP K/sec %CP K/sec %CP K/sec %CP /sec %CP
> kspace9 15998M 96365 20 48302 12 149445 18 113.7 0
> kspace9,15998M,,,96365,20,48302,12,,,149445,18,113.7,0,,,,,,,,,,,,,
>
> kspace9:~ # bonnie++ -n 0 -u 0 -r `free -m | grep 'Mem:' | awk '{print
> $2}'` -s $(echo "scale=0;`free -m | grep 'Mem:' | awk
> '{print $2}'`*2" | bc -l) -f -b -d /raid6
> Using uid:0, gid:0.
> Writing intelligently...done
> Rewriting...done
> Reading intelligently...done
> start 'em...done...done...done...
> Version 1.03d ------Sequential Output------ --Sequential Input- --Random-
> -Per Chr- --Block-- -Rewrite- -Per Chr- --Block-- --Seeks--
> Machine Size K/sec %CP K/sec %CP K/sec %CP K/sec %CP K/sec %CP /sec %CP
> kspace9 15998M 100321 22 48617 13 131651 16 120.2 1
> kspace9,15998M,,,100321,22,48617,13,,,131651,16,120.2,1,,,,,,,,,,,,,
>
>
> ===================================================================================
>
> results for old raid 1:
> a test of old raid 1 which I have done unintended, because I forgot to
> mount
> the raid array :-)
> mounten vergessen
> ---------------------------------------------------------------------
> -> vergleichsresultate :-)
>
> kspace9:~ # date ; cp -r /home/roemke/HHertzTex/OLDER/ /raid5/ ; date
> Fr 1. Jul 16:07:32 CEST 2011 ^^^ not raid 5, old raid 1, forgot to mount
> Fr 1. Jul 16:08:39 CEST 2011
> aehnlich (similiar)
>
>
> test mit bonnie++
> kspace9:~ # bonnie++ -n 0 -u 0 -r `free -m | grep 'Mem:' | awk '{print
> $2}'` -s $(echo "scale=0;`free -m | grep 'Mem:' | awk '{print $2}'`*2" |
> bc -l) -f -b -d /raid5 <-- not raid 5, still the older raid 1
> Using uid:0, gid:0.
> Writing intelligently...done
> Rewriting...done
> Reading intelligently...done
> start 'em...done...done...done...
> Version 1.03d ------Sequential Output------ --Sequential Input- --Random-
> -Per Chr- --Block-- -Rewrite- -Per Chr- --Block-- --Seeks--
> Machine Size K/sec %CP K/sec %CP K/sec %CP K/sec %CP K/sec %CP /sec %CP
> kspace9 15998M 62977 9 34410 9 101979 13 66.7 0
> kspace9,15998M,,,62977,9,34410,9,,,101979,13,66.7,0,,,,,,,,,,,,,
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